In CA (Carrier Aggregation) using a cell #1 (for example, a macro cell) and a cell #11 (for example, a pico cell) in a “Heterogeneous Network” of LTE (Long Term Evolution)-Advanced, one can expect a case where, at an edge of an area covered by the cell #11, the uplink is out of synchronization while the downlink provides good quality, as shown in FIG. 1.
In such a case, it is considered that a radio base station eNB#11 uses the following two methods for continuously scheduling downlink data signals to the mobile station UE.
A first method is a method in which the radio base station eNB#11 allocates no resources for transmitting the uplink data signal (PUSCH: Physical Uplink Shared Channel) to the mobile station UE in the cell #11.
Such a method, however, has a problem that since the mobile station UE must transmit SRS (Sounding Reference Signal) even if the mobile station UE is not assigned a resource for transmitting the uplink data signal by the radio base station eNB#11, the SRS acts as an interference source to the adjacent cell #1.
A second method is a method in which the radio base station eNB#11 deactivates only the uplink in the cell #11 by RRC signaling.
Such a method, however, has a problem of increasing the load to the RRC signaling.
For solving the foregoing problems, in the LTE specification development meeting, a method as shown in FIG. 6 was proposed in which the radio base station eNB#11 independently uses a MAC Control Element for activating and deactivating the uplink in the Scell, and a MAC Control Element for activating and deactivating the downlink in the Scell (see non-patent document 1).